This invention relates to new fluoropolymer containing composites having improved wear resistance characteristics. More particularly, the invention relates to coatings useful in the manufacture of composites which are both flexible and resistant to wear and abrasion. The invention further relates to a novel method for preparing such composites whereby the wear characteristics of relatively hard polymers are imparted to composites, such as woven textile composites, without substantial loss of flexibility.
Perhaps the most well-known subclass of fluoropolymers are substances called "fluoroplastics" which are generally recognized to have excellent electrical characteristics and physical properties, such as a low coefficient of friction, low surface free energy and a high degree of hydrophobicity. Fluoroplastics, and particularly perfluoroplastics (i.e., those fluoroplastics which do not contain hydrogen), such as polytetrafluoroethylene (PTFE), fluoro (ethylenepropylene) copolymer (FEP) and copolymers of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA), are resistant to a wide range of chemicals, even at elevated temperatures, making them widely useful in a variety of industrial and comestic applications. The broad class of fluoropolymers also includes substances called "fluoroelastomers" which are not only elastomeric, but possess to a lesser degree several of the aforementioned physical and electrical properties of a fluoroplastic. Fluoroelastomers, including perfluoroelastomers, however, have a low flex modulus and conformability which is lacking in the more crystalline fluoroplastics.
Fluoropolymers, such as polytetrafluoroethylene, are also well-known for their low coefficient of friction and relatively low surface-free energy which contributes to release behavior. While they exhibit outstanding chemical and thermal resistance, they are soft waxy materials with fragile surfaces easily damaged mechanically by scratching or wearing when rubbed against other materials. It is for these reasons that cookware and other metal surfaces requiring non-stick and/or low friction frequently employ coatings that are combinations of PTFE and relatively harder polymers. Increasing proportions of the harder polymer component in the coating matrix can lead to improved wear characteristics, but with an attendant loss of elongation (embrittlement). While such coating compositions may be reasonably employed on relatively rigid substrates, such as those normally used on coated bakeware, when coated directly onto flexible substrates, such as woven cloth, they result in composites which are most frequently too brittle to serve as flexible products, and even crack when folded upon themselves.
Accordingly, it is an object of this invention to provide a fluoropolymer containing coating for a flexible substrate which will retain its flexibility, exhibit good internal matrix cohesion and substrate to matrix adhesion, and yet possess the improved wear resistant characteristics of the relatively harder polymer coatings, including blends with PTFE.
It is also an object of this invention to provide a fluoropolymer-containing composite which is flexible and possesses good surface wear characteristics, and with the outstanding frictional and release properties of a fluoropolymer.
It is a further object of this invention to provide a method for preparing fluoropolymer-containing composites which exhibit outstanding wear characteristics and a low coefficient of friction.